Generating velocity solutions with globkgeoweb.mit.edu/~floyd/courses/gg/201807_Bishkek/pdf/23-globk_vels.pdf · Generating velocity solutions with globk T. A. Herring 1 M. A. Floyd1

Generating velocity solutions with globk

T. A. Herring1 M. A. Floyd1 M. Perry2

1Massachusetts Institute of Technology, Cambridge, MA, USA2University of Montana, Missoula, MT, USA

GPS Data Processing and Analysis with GAMIT/GLOBK and trackHotel Soluxe, Bishkek, Kyrgyzstan

2–7 July 2018

http://geoweb.mit.edu/~floyd/courses/gg/201807_Bishkek/

Material from R. W. King, T. A. Herring, M. A. Floyd (MIT) and S. C. McClusky (now at ANU)

Overview

• Basics of “velocity” solutions• Invoked with “apr_neu all xx xx xx <NEU velocity sigmas>”

• Strategies for setting up solutions (they can take a long time to run)• Strategies for speeding up solutions.• Methods for “cleaning up” potential problems• Different reference frame realizations• Some examples.• These solutions involve making decisions about how to treat data and

the type of solution to be created – lots of decisions

2018/07/03 Generating velocity solutions with globk 1

GLOBK velocity solutions

• The aim of these solutions is to combine many years of data to generate position, velocity, offset, and postseismic parameter estimates. Not uncommon to have 10000 parameters in these solutions.• Input requirements for these solutions:• a priori coordinate and velocity file. Used as a check on positions in daily

solutions (for editing of bad solutions) and adjustments are a priori values (a priori sigmas are for these values)• Earthquake file which specifies when earthquakes, discontinuities, and mis-

named stations affect solution. Critical that this file correctly describe data.• Process noise parameters for each station. Critical for generating realistic

standard deviations for the velocity estimates (sh_gen_stats).


Velocity solution strategies

• In general careful setup (i.e., correct apriori coordinate, earthquake file and process noise files) is needed since each run that corrects a problem can take several days. Incorrect solutions may not complete correctly and results may be subtly wrong.• General strategy for iteratively generating velocity solution:

• Define a core-set of sites (usually 20-200 sites) where the solution runs quickly. Test files on this solutions and use the coordinate/velocity estimates to form the reference frame for time series generation.

• Time series using these reference frame sites and then test (RMS scatter, discontinuity tests) to form a more complete earthquake and apriori coordinate/velocity files.

• Steps above are repeated, usually increasing number of stations until solution is complete. As new stations are added missed discontinuities and bad process noise models can cause problems.

• Aim here is make sure that when a large solution is run (maybe several days of CPU time) that the run completes successfully.


Before velocity runs

• Surveys may be combined into one solution per survey• No need to re-run glred again to see long-term time series• Multiple “.org”-files may be read by tssum or sh_plot_pos

• tssum ts_pos mit.final_igb08 -R survey1_comb.org survey2_comb.org ...• ts_pos is the name of a directory for the .pos files. (. can be used)

• sh_plot_pos -f survey1_comb.org survey2_comb.org -k ...


Example: Long-term time series for survey sites

Reasonable repeatability

−30

−20

−10

0

10

20

30

Up / m

m

2007 2008 2009 2010 2011 2012 2013 2014

vu = −1.32 ± 3.57 mm/yrWRMS = 3.3 mm; NRMS = 1.00Reference ellipsoid height: −29.1700 m

−8

−6

−4

−2

0

2

4

6

East

/ m

m

ve = −35.30 ± 0.75 mm/yrWRMS = 1.7 mm; NRMS = 1.00Reference longitude: 237.317721286°E

−6

−4

−2

0

2

4

6

Nort

h / m

m

BOLIvn = 18.76 ± 0.71 mm/yr

WRMS = 1.1 mm; NRMS = 1.00Reference latitude: 37.908935678°N

Outlier in vertical

−80

−60

−40

−20

0

20

40

60U

p / m

m

1994 1996 1998 2000 2002 2004 2006 2008 2010 2012 2014

vu = −3.81 ± 0.53 mm/yrWRMS = 49.5 mm; NRMS = 1.00Reference ellipsoid height: 14.3568 m

−6

−4

−2

0

2

4

6

East

/ m

m

ve = −24.58 ± 0.13 mm/yrWRMS = 2.1 mm; NRMS = 1.00Reference longitude: 237.593225287°E

−3

−2

−1

0

1

2

3

4

5

6

Nort

h / m

m

0412vn = 4.19 ± 0.14 mm/yr

WRMS = 0.9 mm; NRMS = 1.00Reference latitude: 38.441137077°N


Excluding outliers or segments of data

• Create “rename” file records and add to globk command file’s “eq_file” option, e.g.rename PTRB PTRB_XPS h1407080610_nb4arename PTRB PTRB_XPS 2014 07 07 18 00 2014 07 08 18 30rename ABCD ABCD_XCL 2013 07 08 00 00

• “XPS” will not exclude data from glred (so still visible in time series) but will exclude data from globk (combination or velocity solution)• “XCL” will exclude data from all glred or globk runs


Run globk

• Create new “.gdl”-file with combined binary h-files, e.g. from vsoln/, assuming standard directory hierarchy• ls ../*/gsoln/*.GLX > vsoln.glx.gdl

• Optionally run glist to see size of solution• Recommended to prevent problems during long globk run• glist can read earthquake file and globk use site type commands.

(Useful if a globk solution seems to be missing or has extra sites.)

• Run globk• This may take many hours for very large/long velocity solutions• Use tsfit with earthquake file to generate a priori site coordinates. Be

careful if ~/gg/tables/itrf08_xxx.apr files also used because some site names permutations may have inconsistent coordinates (use unify_apr to be safe)


glorg for different reference frames

• No need to re-run globk every time you want• glorg is usually called from globk command file (“org_cmd”

option) but glorg may be run separately• globk 6 globk_vel.prt globk_vel.log globk_vel.gdlglobk_vel.cmd

• glorg globk_vel_noam.org ERAS:… glorg_vel.cmd vel.com

• Must have saved the “.com”-file!• e.g. “com_file @.com”• Do not use “del_scra yes” in globk command file• “apr_neu” must be loosely constrained (“apr_rot” and “apr_tran” will also

need to be used for sestbl. “BASELINE” experiment solutions).


Use of equates

• With earthquakes and discontinuities, there can be many site names for the same physically location:• Equate commands in glorg allow the velocity adjustments at these sites to

be made the same (or constrained to be the same within a specified sigma)• “eq_dist” allows site separate by distance to equated (and constrained in

latest glorg).• “eq_4char” equates sites with same 4-character name (useful to stop

equates at sites that share antennas).• Chi-squared increments of equates allows assessment of equates (use

“un_equate” for large chi-squared values)• Use “FIXA” option to make a priori the same for equated sites (better to use

consistent a priori file).


Uses of sh_gen_stats

• Velocity solutions are often iterative:• Generate time series using some reference frame sites (IGb08 sites initially

for example).• Fit to the time series (tsfit) to:

• Find outliers, nature of earthquakes (log needed?), discontinuities• Self consistent a priori file.• Used FOGMEx model (realistic sigma) to get process noise model and list of low-

correlated noise reference frame sites). Use “stabrad” option for dense networks• Run globk velocity solution to refine reference frame site coordinates and

velocities• Re-generate time series and repeat.


Some comparisons: Approach

•Use sh_exglk -f <soln.org> -vel<soln.vel> -rmdupto extract velocity estimates (rmdup removes equated sites with the same estimates)•Program velrot allows fields to be compared

(change frames and merge fields as well). For example:velrot solna.vel nam08 solnb.vel IGS08 ‘’ ‘’ ‘’ ‘’ Ncompares to solutions directly (use “RT” instead of “N” to allow rotation and translation rates). Use grep ‘^S ‘ to get statistics.


Comparisons: Decimation

Decimation: Different days of week (1996-2015 solution, small subset of sites):Un-aligned fields

compare 1 NMT_vel_150418_day1.vel NMT_vel_150418_day3.vel

S Component North # 75 WMean -0.00 WRMS 0.04 mm/yr, NRMS 0.198

S Component East # 75 WMean -0.02 WRMS 0.04 mm/yr, NRMS 0.203

S Component Up # 75 WMean 0.03 WRMS 0.16 mm/yr, NRMS 0.180

S Component Horz # 75 WMean -0.01 WRMS 0.04 mm/yr, NRMS 0.200












Comparison: Time series vs GLOBK

• PBO Combined analyses:Un-aligned fields (no rotation and translation).

compare 1 PBO_vel_150425.vel PBO_vel_150425KF.vel





compare 4 PBO_vel_150425.vel PBO_vel_150425_NAM08.vel

S Component North # 1972 WMean 0.03 WRMS 0.13 mm/yr, NRMS 0.965

S Component East # 1972 WMean 0.02 WRMS 0.15 mm/yr, NRMS 1.049

S Component Up # 1972 WMean -0.07 WRMS 0.41 mm/yr, NRMS 0.943

S Component Horz # 1972 WMean 0.02 WRMS 0.14 mm/yr, NRMS 1.008

compare 7 PBO_vel_150425KF.vel PBO_vel_150425_NAM08.vel

S Component North # 1969 WMean 0.04 WRMS 0.16 mm/yr, NRMS 0.952

S Component East # 1969 WMean 0.02 WRMS 0.17 mm/yr, NRMS 0.967

S Component Up # 1969 WMean -0.08 WRMS 0.44 mm/yr, NRMS 0.935

S Component Horz # 1969 WMean 0.03 WRMS 0.16 mm/yr, NRMS 0.959

PBO_vel_150425.vel: tsfit solution to time series

PBO_vel_150425KF.vel: tsfit Kalman filter solution to timeseries

PBO_vel_150425_NAM08.vel: GLOBK combined velocity solution (NMT+CWU), decimated 7 days, 28-subnet combination. Reference frame realization to NAM08 frame sites (~600)

See Herring et al., Reviews of Geophysics, 2016 for more detailed comparisons.


Final comments

• Practice large solutions with decimated data sets and small networks (run time increased cubically with number of stations)• Make sure your a priori coordinates files are consistent (especially

with equates)• Use the out_aprf command in tsfit to generate an apriori which is consistent

with your timeseries estimates.


Documents

Generating velocity solutions with globkgeoweb.mit.edu/~floyd/courses/gg/201807_Bishkek/pdf/23-globk_vels.pdf · Generating velocity solutions with globk T. A. Herring 1 M. A. Floyd1